This invention relates to transducers in general and more particularly to a supporting structure or header for a semiconductor transducer.
Pressure transducers have been widely employed in the prior art for various applications and in various environments. Accordingly, the prior art is replete with a number of patents which employ semiconductor pressure transducers which transducers utilize piezoresistive elements as the force reponsive members. By utilizing the semiconductor transducer, the prior art is enabled to provide a reliable structure which is relatively inexpensive to fabricate and construct while exhibiting reliable operation.
As one can ascertain, such transducers have been employed in different environments which environments subject the transducers to stringent operating conditions such as high temperatures and high pressure while also subjecting the transducer to deleterious substances. For example, such transducers have been used in the automotive field to monitor engine pressure and so on. They are used in the aircraft field to measure aerodynamic pressures. In addition, they are used in many other fields. Apart from the high operating temperatures, the transducers have been subjected to various pollutants and gases which are present in such environments.
It has been a major object of the prior art to provide a reliable transducer which is inexpensive. A major problem in providing such a transducer relates to the support or header for the device. Additional problems relate to economically and reliably affixing lead wires to the small silicon pressure sensing chips used in such transducers. Essentially, a semiconductor pressure transducer comprises an arrangement of piezoresistors which are formed on the surface of a relatively thin diaphragm. The diaphragm which may be fabricated from a semiconductor material or a glass is relatively fragile and must be supported to enable operation. As one can ascertain, the diaphragm is subjected to a pressure or force and deflects according to the magnitude of such pressure. The deflection of the diaphragm causes a change in the resistance of the piezoresistive elements which elements provide an electrical signal proportional to the magnitude of the applied pressure or force.
As indicated, such diaphragms are relatively fragile and are typically supported by a conventional housing or annular structure. For examples of typical support mechanisms for such diaphragms, reference is made to U.S. Pat. No. 4,216,404 entitled HOUSING AND LEAD ARRANGEMENTS FOR ELECTROMECHANICAL TRANSDUCERS, issued Aug. 5, 1980 to A. D. Kurtz and Joseph R. Mallon, Jr. and assigned to Kulite Semiconductor Products, Inc., the assignee herein. Reference is also made to U.S. Pat. No. 3,654,579 entitled ELECTROMECHANICAL TRANSDUCERS AND HOUSINGS, issued on Apr. 4, 1972 to A. D. Kurtz, Joseph R. Mallon, Jr. and Charles Gravel and assigned to the assignee herein.
These patents show various annular members which are used to support a semiconductor pressure transducer and, essentially, are employed to enable the transducer to be used in a typical application. Based on developments made in the transducer technology, new diaphragm configurations have been employed to achieve higher outputs while providing more reliable operation over wide pressure and temperature ranges. An example of a typical structure is shown in U.S. Pat. No. 4,236,137 entitled SEMICONDUCTOR TRANSDUCER EMPLOYING FLEXURE FRAMES, issued on Nov. 25, 1980 to A. D. Kurtz, Joseph R. Mallon, Jr. and Timothy Nunn and assigned to the assignee herein. This patent shows a pressure transducer which employs a semiconductor diaphragm with a top surface having a central boss area of a trapezoidal cross section which is surrounded or framed by a continuous groove. Peripheral sensors are formed on the bottom surface of the diaphragm with a first sensor adjacent the outer edge of the groove and another sensor parallel to the first sensor and adjacent to the inner edge of the groove.
In this structure the groove operates as a stress concentrating area to enable the sensors to provide a relatively large output upon application of a force to the diagragm. Essentially, such devices are relatively small and have to be supported and positioned in a transducer housing in a reliable and efficient manner. It is also very important to effectively isolate the silicon transducer element from the influence of any external stresses. Such stresses may be of mechanical origin or induced by a mismatch in thermal expansion between the silicon and associated materials. Thus it is important in using such structures to employ a header or support housing for the transducer which is extremely rugged, which does not vary in characteristics over wide temperature ranges and which structure will enable the rapid coupling of output leads from the transducer assembly to an external connector to enable efficient fabrication of the final transducer unit. The structure must have an expansion coefficient which is close to that of the semiconductor material.
The housing or support structure should further possess good reliable operating characteristics over a wide temperature range and serve as an efficient insulator member to thereby insulate or electrically isolate the diaphram and associated lead wires from the external environment.
A main purpose of the header or housing is to enable the rapid connection of leads from the transducer assembly to the external connector.
Metal housings are often employed. However, such housings have serious limitations. Metal is a conductor and coatings must be applied to insulate the lead wires from the housing structure. The coatings are expensive to apply and sometimes fail in service. Also metal cannot be used to perfectly match the thermal expansion of silicon over a wide temperature range. For instance, steel has a much higher expansion than silicon and introduces undesirable thermal stresses. Iron-nickel alloys are better and such alloys as Invar and Kovar are sometimes employed but even these materials match imperfectly and only over a limited temperature range.
It is an object of this invention to show a structure which can be inexpensively and reliably manufactured from such a desirable material as borosilicate glass.
It is, therefore, an object of the present invention to provide a header assembly for a pressure transducer which assembly is easy to fabricate and which possesses the ability to allow rapid lead connection while further providing to isolate the diaphram assembly as above indicated.